So, if the memory unit is not a listed storage device, make sure the memory unit is fully inserted into the memory unit slot on the front of the Xbox 360 console. Try the other memory unit slot to make sure that is not the problem. If you have a second memory unit, try it out as well to determine whether the original memory unit is faulty or not.
Please note: Damaged memory units will not appear in the Xbox Dashboard and could harm your Xbox 360 console. Memory units that have been crushed, immersed in liquids, or exposed to intense heat may be damaged beyond use and will not appear in your list of storage devices. So don’t get too pushy or things might get even worse!